Quote ryan mead: I would like
something that gets out of the way automatically when my wife opens the door so that she
doesn't think I've gone into bar-the-door-shut, goddammit-I'm-creating-don't-bother-me
mode just because I've put a bass trap in place.

Great one! Yeah, I feel your pain man! And you never
liked her mother either, and that belt she was wearing last night made her butt look huge!
How could you??? And now, you want to lock yourself up in your little kingdom and totally
ignore her... etc... You are a cad, sir!

Been there, done that, got the
T-shirt!

You're on your own there,
mate!
I'm just trying to be sensitive, to prevent my sweet sensitive bride (can you tell we're
newlyweds?) from feeling like this...

...which I suspect she would if it seemed to her
that I'd braced the door shut behind me.

(But yeah her mom is a handful
sometimes.)

Quote
Doublehelix:The "automatic" bit is going to take a bit of work on your
part... good luck! I am anxious to see what you come up with.

No guarantees it'll work out that way though.
The default plan is just a flat stationary 20cm-deep trap behind the door.

Quote Ian Savage:A
tuned-membrane trap won't take up much more space than a broadband bass trap (takes up
less than one that goes appreciably low), they can't be that hard to build, as I made one
once
- hardest bit was getting it properly sealed.

Care to elaborate? What
frequency were you after, what did you use for materials (plywood's easy to source; so are
vinyl flooring and carpet), what were the final dimensions, and how did you end up sealing
it (silicone)? Did you damp it on the inside?

Also, for the silent among you
out there, anyone else with any experience building a panel (or Hemholz for that matter)
trap?

Right, have dug out my old design drawings! My memory's terrible, so I'll just quote
verbatim from my scribbles:

For a diaphagmatic absorber, resonant frequency =
170 / sqrt(md), where m=the surface density in lb/sq ft, and d=the depth of the airspace
in inches. I can't remember offhand exactly how putting rockwool or similar in the
airspace affects the maths, but it obviously makes the thing more efficient. I believe I
gave up on the diaphragmatic design in the end though, because if it's not TOTALLY sealed
it causes more problems than it solves. And I couldn't get the bastard totally
airtight.

For a perforated slat absorber, which is what I eventually ended up
with, resonant frequency = 5.5 x sqrt(% perforation/(d x D)), where d = slat depth (m), D
= cavity depth (m), and the % perforation for a slatted box can be worked out by (r/(w+r))
x 100%, where r=slat spacing and w=slat width.

What it looks like is in the
bottom right-hand corner of this picture:

Basically the gap between each slat acts as a tuned Helmholtz
resonator, sort of like blowing across the top of an empty bottle, with the airspace
behind them (usually including some rockwool or similar, which broadens the peak of the
absorbtion) acting as a 'spring' and soaking up some of the wave energy.

The
trap I built was aiming for knocking out a standing wave at about 110Hz in a small room,
so with the materials available I settled on using planks of wood 150mm wide by 38mm deep,
and made the cavity 200mm deep (like yourself, I simply didn't have the room to go much
deeper!). The slats were spaced 5mm apart, with the back 100mm of the cavity padded with
Rockwool.

Plugging in the numbers, you get a resonant frequency of 5.5 x
sqrt(3.2% / (0.038 x 0.2)), which gave me 111.5Hz. Sadly I didn't have the equipment to do
objective measurements of the difference it made, but subjectively it had a massive effect
on the booming at the low-ish end of the spectrum.

Give me half an hour or
so and I'll see what can be done to attack 45Hz with common materials without making
anything too massive! Obviously the thicker the slats and the deeper the cavity, the lower
the resonance though.

I got a lot of my background from a BSc in Audio at
the University of Salford, and then later found out that the lecturer in acoustics had
leaned heavily on a book called 'The Master Handbook of Acoustics', by F. Alton Everest. I
recommend it heartily, it'll be the best twenty quid you ever spend on acoustic treatment.
As long as you don't mind working in imperial measurements, which do my fruit, hence the
conversion to metric above.

Quote Ian Savage:the lecturer in
acoustics had leaned heavily on a book called 'The Master Handbook of Acoustics', by F.
Alton Everest. I recommend it heartily, it'll be the best twenty quid you ever spend on
acoustic treatment.

Funny you
should mention it-- I have the book right here! I bought it about two years ago on a trip
back home, but haven't paid any attention to it until recently. (In a weird turn of dumb
blind luck, I bought two then-unknown-to-me books on audio-- the other one was Bob Katz's
book.) I put myself to sleep last night with the section on tuned traps and a couple
glasses of red.

Quote Ian
Savage:I can't remember offhand exactly how putting rockwool or similar
in the airspace affects the maths, but it obviously makes the thing more efficient.

Here's the part that scares me-- both
Everest's book and Paul White's article say that putting rockwool in the airspace lowers
the resonant freqency "somewhat", but they're both vague on that point. (I see
experimentation and material waste ahead... )

Quote Ian Savage:

As long
as you don't mind working in imperial measurements, which do my fruit, hence the
conversion to metric above.

No
worries there and no need to translate for me! As a Canadian I was brought up with
imperial, and then forcefully converted to metric along with the rest of the country when
I was a kid, so I'm comfortable with both, but imperial's in my soul. I'm living in
metric land now, though, so I'm just rolling with it. I can't even find a ruler or tape
measure with inches on it!

Anyways, please don't take it personally if I opt not to go for some kind of tuned
trap-- it DOES sound like there are rather a lot of pitfalls there.

Well, I've decided to make the behind-the-door
trap a broadband trap, hinged to the door. When the door is closed, the trap should sit
like this:

And when it's open it should sit like
this:

In both pics, the four-sided piece of
plywood is the baseplate/top plate for the trap, showing the eventual vertical
cross-section, and the yellow arrow shows where I'll hinge the trap to the door.

I considered making another 45-degree angle so that the distal face of the trap
would sit flush against the wall when the door is closed, but decided against it because
that would have cut down on the size of the trap considerably and moved it much closer to
the wall. A blunt square distal end may be less elegant, but more effective!

I'll also mount four casters to the baseplate and put some kind of track in the ceiling,
with a pin or roller on the trap that rides in the track so that it automatically moves
into place when the door is closed. At least that's the plan.

You can also
see a triangular offcut of wood in the corner of the room in both pictures that represents
where I can stuff a bit more rockwool into the corner somehow (I'm thinking just sewn bags
stuck into the corner) so that this thing behaves a little more like a proper
superchunk.

Here is a little more evidence that I've actually started working
on this trap:

If anyone sees anything amiss,
please speak up! It's bedtime in Seoul so there is time for me to make refinements (or
wholesale redesigns!) on the basis of your comments!

Meanwhile, I've made a
stand for the whaleTrap:

There's some painfully obvious levelness
issues, but I've tweaked the stand a bit to hopefully address them. And anyways I don't
think the standing waves will give a damn if it's level or not.

I'm getting very close to being ready to convert my temporary woodworking shop back into
a studio, and my wife is VERY ready to see all of the completed traps disappear from the
living room! If the frequency response curve ends up looking anything like the one on the
first page, I'm going to have a breakdown or something...

Quote ryan mead:It was suggested
to me in an email awhile back (from the good folks at Ready Acoustics) that I replace the
front blinds with some heavy and bulky curtains.

It sounds like a good plan,
but it also sounds like another step towards converting my studio into a sauna.

Thoughts?

Nobody then?

If you look at the graph on the first page of this thread, I think I've got
obvious high-frequency issues. I've noticed that in some Studio SOS's they put up Auralex
on the wall behind the speakers, and in others they don't. It's not a mirror point per
se, so I'm not clear on how important this is.

There has been a lot of head-scratching, fussing,
and material waste over the behind-the-door trap, and in the end it doesn't seem to have
panned out so well. I haven't even tried to hinge it to the door yet, but it's far too
heavy to be expected to behave properly when the door is opened and shut. Besides, I'm
having a hard time tracking down the closet door mounting hardware that I thought would be
suitable for a ceiling track. Koreans aren't into bifold closet doors, they're into
standalone wardrobes.

For the time being I guess I'll just leave it flat
against the wall when composing, arranging, and woolgathering, and shut the door and go
into wendy-let-me-explain-something-to-you mode (seriously, she'll think
it's because I don't want her to intrude, not because I'm trying to get rid of that 90Hz
notch) when I'm finishing off a mix.

Anyways-- the transition from wood shop
to music room is underway! Here are
the back and front walls:

In the first picture, you can see
the behind-the-door trap, slouching disappointedly against the wall. Asymmetry
is somewhat tolerable at the rear of the room, right?

At this stage I stood
at the mixing position and clapped my hands in front of my face. There was an awful ring,
but I don't have any of the mirror point traps up yet so I'm not going to lose any sleep
over it tonight.

I did try clapping again when the ceiling trap was leaning
against one of the side walls, and the ring seemed to have subsided somewhat, so we'll see
what tomorrow holds.

These lights originally came
with this irritating switch, which I bypassed:

(before)

(after)

The first test of the room's new acoustics
might come as early as tomorrow! I've
still got my four RealTraps to play with to do some fine tuning, though I'm pretty sure
one's going to wind up at my feet under the desk, where it made a huge improvement at the
outset.

I've noted a problem already. The whaleTrap resonates at a really low frequency. (I
noticed when I was sitting on the sofa with a beer, idly banging my head on it last
night.) A nice long note like an acoustic bass.

I'm thinking it's because I
mounted this cleat too close to the trap, pinning it to the wall, and perhaps coupling it
to the ceiling panel (which also resonates). There's no need for the cleat to be touching
the trap-- it's just for safety in case the trap decides to fall forwards-- so I'm going
to move it forward until they're not touching, and hope this resonance goes away.

Meanwhile-- the sub showed up!
I
know I've been advised against it in this very thread, but I couldn't resist. I've got a
choice between two ways of hooking it up:

1) via the crossover in the sub

This option would presumably split the signal between the sub and the K&H's
optimally.

2) independently, via the presonus monitor controller

This option would have the advantage of making it easy to turn off the signal to the sub
with the press of a button. I would then set the filter on the sub to match the low end
of the K&H's as best I could. Jury's out on that one.

Seems to be coming along nicely man! Shame about the behind-the-door trap, but we lives
and learns; as regards the sub, that's a tricky one. For optimum sound quality you really
ought to be running the signals in and out of the subwoofer - but does the Presonus have a
dedicated sub-out that'll have its own crossover?

Quote Ian
Savage:does the Presonus have a dedicated sub-out that'll have its own
crossover?

It has something kind
of like a separate sub out ("C" out can be toggled on and off, independently of A and B
outs), but afaik with no crossover. If I go that route I'll try and match the low-pass on
the back of the sub to the low end of the K&H's (which is about 60Hz). I think I'll
run the K&H's through the sub's crossover to begin with, do some testing, and then try
things the convenient but dangerous way, through the Presonus, and see how much worse the
results are. Not quite sure how to set up a test for phasing problems at the low end,
however, or if my ears are good enough to catch such problems myself.

Meanwhile I removed the cleat from in front of the whaleTrap and it still resonates like
a timpani.

There never seems to be an end to the issues, is there? I keep running
into them just when I think I am about done myself!

Regarding the window...

I ended up having to cover my CR window with a small bass trap, even though I was
really looking forward to the natural light. It was a necessary evil in order to get the
sound tamed down to where I am able to mix in the place. It really sucks, but once things
get rolling here in the next month or so, I hope take it down during tracking, and then
hang it back up during mixing.

That may end up backfiring on my since I need to
be able to judge mic placements and choices, and if I compromise my acoustics during
tracking, I may lose the ability to make those choices appropriately.

I bring
this up for 2 reasons:

1) You might need to do what you need to do if you find
you still have a big problem with the window. Sometimes, it is a difficult choice, but you
have to be able to live with the consequences. I wasn't, so I reluctantly covered the
window.

2) Your behind the door corner trap might need to be there for more
than just mixing. It may become the "anytime I am in the studio" trap rather than the
"mixing" trap.

Another option for your window: RPG makes something called a
"ClearSorber" which can go over a window and still let light through. Max from this forum
pointed it out to me as an option, but at the time it was a bit too pricey, and I needed
to get something going ASAP. I might consider replacing my current trap with a ClearSorber
someday. You might want to ask Max about it, I think he has some experience with them.

Regarding the behind-the-door trap: Bummer that your design didn't work out.
Is there anyway you can make it lighter? Minimal framing and maybe make a trap-in-a-bag
type of design to reduce the weight? Is the door solid or hollow? You could always get a
more solid door and then get some heavy-duty hinges if need to. Otherwise, I would just go
with the movable trap. Maybe put some casters on the bottom so that it will move easily
out of the way? Also, consider a small chain and hook system so that when it place, it
will not accidentally fall down and kill any small children or animals if anybody opens
the door when it is in place!

Otherwise, it is looking nice, and coming
right along! Keep it up man!

--------------------James
"Never interrupt your enemy when he is making a mistake" ~Napoleon Bonaparte~

If you run it through the
Presonus CS, the obvious advantage is the ability to bring it in and out of the mix for
comparison purposes. The big disadvantage is the lack of a cross-over. (I know you already
mentioned both issues, just re-iterating for completeness!).

My opinion is that
you should not run the system without a crossover. Good filters will work (that is what a
crossover is after all), and if you have them built-in to the sub, great. I would however
consider having both the mid/highs and the sub on filters... HPF on the mid/highs and LPF
on the sub. You will losing a lot of energy if you don't. Maybe you could invest in a nice
stereo crossover, and use one side for the sub, and one side for the mid/highs???

Anyway, FWIW, that is what I would do, otherwise, I would use the crossover in the sub.
For me personally, I would never just use the CS without some kind of filtering on both
sets of speakers.

--------------------James
"Never interrupt your enemy when he is making a mistake" ~Napoleon Bonaparte~

Belated thanks for the very thoughtful reply. I've been sidetracked
by some problems with my new/used monitors, for which I've started another, very sad, thread.

about the window: I've sent RPG an email, but I'm so over budget at this point that I'm
thinking of just replacing the vertical venetians with a duvet mounted on curtain rings.
Then I could easily let some light in when I'm arranging, and close the curtain when I'm
mixing. (I don't actually record that much.)

about the behind-the-door trap:
Well, the casters part is working, so it is easy enough to roll it into place after
closing the door. Over the next while it'll be one of the variables I test: door open,
door shut and trap flat against the wall, door shut and trap pulled into place. I'll see
how much difference it makes.

about the sub: There's this really harsh
language in the owner's manual:

This seems like a really stupid way to
configure a crossover to me. Who in the hell would want to dial in overlap or a gap?
Moreover, the 80Hz point isn't even indicated on the crossover frequency knob. There
doesn't seem to be much advantage to running the speakers through the sub; in fact the
only effect seems to rob the speakers of their low end. Got any suggestions for a stereo
crossover?

Well, I started testing again, and at first I was pretty depressed because I still had a
big knife-slash at around 90Hz and a big ugly rolloff at the top end. Then I decided to
take some advice from page 1 of this thread:

Quote young david:

If you haven't already done
this, I'd start by experimenting a bit with moving the listening position a foot or two
along the lengthwise dimension. Might help with the bump around 46 and your 90-100
dip.

Quote Jim Y:Would it not be
better to experiment with desk/speaker position before putting any traps in? - That way,
changes for the best with these positions will be more apparent, and you can then position
your traps to suit the room with all your equipment in place.

The following graph shows measurements
taken with the mic at varying distances from the front wall.

Now I'm confused!! I get the
smoothest low end when I position my head as close as possible to the middle of the room!!
This so contravenes the conventional wisdom I've learned here that I'm almost afraid to
post it.

I've done some other tweaks since then-- I have found that I get
a smoother top end with the speakers out about 55cm from the front wall, and my body a
little forward of the exact center of the room.

I've also done a little
Paul-White-style crawling around and determined that the bass response is the least lumpy
with the sub on the floor to the right of the right speaker, and slightly forwards of it.
There was a phase issue, which you can see here: the top curve is without the sub, the
middle curve is with the phase switch in the 0 position, and the bottom curve is with the
phase switch in the 180 position.

I tried to move the sub as close to myself as
possible but it doesn't seem possible to get it as close as the nearfields, so I think
I'll just use it for fun, and make critical bass mixing decisions using headphones, or
with the sub switched off.

I ended up not using a crossover at all.
Subjectively, the information below 80Hz seems so much tighter and more accurate coming
from the K&H's than from the sloppy Tannoy sub, so I just set the high pass for the
sub to about 50Hz, to use the low-end response of the K&H's as a natural kind of
crossover.

Despite the fact the room sounds a great deal tighter and less
boomy now than it did at the outset, even with the sub, I'm kind of disappointed with how
little the frequency response has changed-- and more and more confused by the results of
tiny tweaks...

One more piece of advice I'm going to have to follow:

Quote young david:Final tip
would be once you've settled on the layout, print your room eq graph and stick it on the
wall.

I had a friend with a nice DSLR and wide-angle lens come over the other day, so thought
I'd bump this thread with a couple vanity shots.

The only technical inaccuracy shown above is
that I play the guitar facing the other way when recording, because it picks up less noise
that way.

The astute of you might notice the ergonomically sad position of my
MBP. Next time it's an iMac!

And here's our obliging photographer on the
obligatory chill-out couch...

I'm pretty happy with how the room sounds. I
don't think the frequency response tells the whole story, as the room subjectively is
quite non-resonant without being oppressively anechoic, and I seem to be making good
mixes. Here's hoping we don't get kicked out at the end of our lease!